1. Field of the Invention
This invention relates to roll film cameras and more particularly to a protective mechanism for use in such camera having a back cover operated to load and unload a film magazine into and from a chamber therefor within the camera body. The mechanism of the present invention makes it possible to open the back cover when the exposed film is rewound onto the supply reel within the magazine and to leave the film unrewound by a limited terminal length even when a motor drive unit is used to perform the rewinding operation.
2. Description of the Prior Art
The prior constructions of locking mechanisms for roll film cameras in one form include a control knob accessible from the outside of the camera housing and arranged upon upward manual movement to open the back cover and upon downward movement to become capable of locking the back cover in the closed position. In another form, the locking mechanism is operatively associated with a film rewinding crank for controlling opening and closing operation of the back cover.
With such manually operable locking mechanism, therefore, the operator is required to rely upon his own sense of feeling to detect the slight shock felt by his fingers operating the film rewinding crank just when the terminal end of the film passes from the sprocket before the crank is stopped from further rotation and then moved upward to open the back cover. Otherwise, the film will be fogged at a portion left unrewound into the magazine. Because of difficulties in distinguishing this shock from others, beginners and amateurs of insufficient experience are liable with high probability to open the back cover before the rewinding of the film has been completed. Aside from his difficulties in determining the completion of the rewinding operation, the average operator is liable to perform accidental manipulation of the locking mechanism with the result that a large number of film frames are photographed in blank, or wasted. In order to avoid such faulty operation it has been the common practice to rotate the handcrank in excess with the film entirely retracted into the magazine. In this case, however, it is necessary to break the magazine in order to extract the film before the film is processed.
It is an object of the present invention to provide an improved camera of the roll film type in which rewinding of the exposed film is a necessary prelude to removal of the film magazine.
Another object is to provide an improved camera of the type described with a mechanism for protecting the film from fogging when the magazine is removed.
To achieve this, in one embodiment a sensing mechanism detects whether or not the film is left unrewound onto the supply reel in the magazine and the result of the detection controls the actuation of locking means for the back cover of the camera.
Still another object is to provide a protective mechanism of the character described which also serves to automatically open the back cover when all the picture frames have been retracted into the magazine as the rewinding crank is operatively connected to the locking means.
A further object is to provide an improved motor driven camera of the type in which the back cover can not be opened until all the effective picture frames have been retracted into the magazine and in which the film rewinding shaft can be driven by the motor until that particular time.
A further object is to provide a protective mechanism capable of leaving the film unrewound by a limited terminal length which serves as the grasping end of the film in the later film processing operation.
These and other objects and features of the present invention will become apparent from the following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawings in which: